Electromagnetic radiation may be confined and directed effectively by means of known transmission line structures such for example as microstrip structures. The transmission line structures generally have a narrow conducting strip or strips separated from a larger ground plane by an intermediate dielectric medium. The electromagnetic propagation characteristics are determined by the physical dimension of the conducting strip or strips, and the thickness and electrical properties of the dielectric medium. The propagation velocity along the transmission line structure, for example the microstrip, is determined not only by the geometry of the transmission line structure, but also by the influence of any elements that may be electromagnetically coupled periodically to the transmission line. Conventionally, propagation delay may be controlled incrementally through the incorporation of extended lengths of line, typically in coiled or meander form. The overall propagation delay is determined through switches to direct the passage of propagated energy along selected lines.